1. Field of the Invention
The present invention relates generally to motors used in downhole drilling applications, and in particular, to downhole drilling motors that may be subjected to unusually high levels of bending stress, such as used in very deep and very extended lateral drilling operations. The downhole motor described herein has internal structures intended to improve its reliability and lengthen its intervals between servicing.
2. Description of the Related Art
Downhole drilling motors used in the oil and gas drilling industry typically include a drive shaft assembly connected between a power section and a bearing section. The drive shaft transfers torque from the eccentrically rotating power section to the concentrically rotating bearing assembly to rotate a drill bit as it is pushed against the earthen formation, effecting a drilling action.
The motor is often configured such that the axis of the power section is angularly offset from the axis of the bearing section and drill bit. The driveshaft assembly may include universal joints, or alternately ‘flex’ joints, on either end to accommodate the mis-alignment of the axes during a drilling operation while allowing transfer of torque from the power section of the motor through the bearing assembly and out to the drill bit.
During operation, drilling motors are often subjected to extreme, cyclic bending loads, and also rapidly varying compressive loads. In these applications, it may be difficult to maintain the internal components of drilling motors in their proper orientations. Shifting of these components during operation may result in sudden, premature and catastrophic failure of the motor.
A stabilizer is a drill string component well known in the art that typically has a plurality of blades, or raised portions of material, that extend radially outward from a main tubular body. The blades may extend to a diameter that is slightly less than the diameter of the wellbore. This configuration may permit the stabilizer to travel through the wellbore, while ensuring that the axis of the stabilizer is kept nearly concentric to the axis of the wellbore. The deflection of the drill string at the stabilizer location may, therefore, be limited to that permitted by a gap between the stabilizer blades and the wellbore. Because the outer surfaces of the blades may continually contact the wellbore due to side loading, these surfaces may be coated with abrasion-resistant material to reduce wear. The areas between the blades may form open channels that provide pathways to allow annular flow to pass by the stabilizer.
One type of stabilizer is a drill string component having top and bottom connections that connect to upper and lower components within the drill string. Another type of stabilizer is in the form of a threaded sleeve that threads to the outer diameter (OD) of one of the drill string components; for example, the lower stabilizer of a mud motor which is typically threaded to the OD a bearing assembly housing. The threaded sleeve option may allow interchangeability between stabilizers of different diameters, depending on the hole size and the amount of clearance desired.
Despite the advancement in drilling technology, there remains a need for advanced techniques for reinforcing drilling equipment. The present invention is directed at providing such advanced techniques.